This invention relates generally to hydraulic clamping apparatus and, more particularly, to hydraulic clamping apparatus for injection molding machines.
According to typical prior art hydraulic mold clamping systems, a small quick feed cylinder is retained by the ram piston of a large high force cylinder. Thus, during a quick feed stroke of the mold produced by the small cylinder, the large ram piston must also move. This factor undesirably entails the flow of large oils volumes to the large cylinder. In some systems this results in loss of power and often requires costly special buffers in the hydraulic circuits to switch clamping speed and to prevent shocks at stoppage. In other systems, the large oil flow creates air bubbles that cause the apparatus to produce unacceptable finished parts. In addition, the requirement for rapid, lengthly movement of the large ram piston substantially increases both machining and repair costs of the apparatus.
Many of the above disadvantages are obviated by mold clamping systems disclosed by Japanese Utility Model Nos. 46-9264 and 49-44064. Disclosed thereby are mold clamping arrangements in which a small diameter piston reciprocates independently of a large diameter ram piston to provide quick feed movement of a mold. Subsequently, a clutch mechanism engages the ram piston which then provides a short stroke that results in a high closure force on the mold pieces. Although offering some improvement, these systems also suffer deficiencies including the requirement for high pressure seals subject to lengthly quick feed piston strokes, the requirement for replacing clutch mechanisms when mold sizes are changed and problems associated with accurately repeatable clutch mechanism movement. Many of those deficiencies are eliminated by apparatus disclosed in U.S. Pat. No. 4,545,756. However, the clamping apparatus disclosed therein exhibits an overall size that is undesirable for certain applications.
The object of this invention, therefore, is to provide an improved hydraulic clamping apparatus for injection molding machines.